Difficult Bonding , am I making progress?

Hello, I am currently trying to bond my grumpy female lion head bun with a beautiful mini rex ( rescue bun) . They have been living in adjacent cages for 5 weeks now, initial 2 weeks with double mesh between them and the last 3 weeks with single mesh. At first there was lots of aggression from her, but this has since settled down. They are happy to eat and groom themselves in front of each other, touch noses nicely and I even saw her grooming his nose through the bars today. She is, however, notoriously grumpy, confident and has attitude. She was bonded for a year to her little hubby, but he died suddenly before Christmas. I have also been switching litter trays, toys and eventually buns into each other spaces so they get used to each other's scent.
I have , over the past couple of days been putting them together in a neutral space with a couple of hay boxes, and some hiding places and new toys to see if they will bond.
It seemed to be going well, as they fluctuate between ignoring and chasing/nipping/lunging. However on their second date today, she was quite interested in him, in a sort of friendly way, but he is just terrified and spent the entire time cowering in his hay box, eyes bulging and really unhappy. There was no evidence of mounting or grooming ...they did both nibble on the hay, but she was very confident and easy in the new space, and he was terrified of the space and of her. I am worried he wont make a move as he is too frightened of her. I intend to do these sessions each day until there is a break through as I know the patience is key, but am I wasting my time if he is too terrified?
They are both about the same age and are neutered.

I don't have much bonding experience - only once - but from what I have read, I would be very patient and just try to ease them into it. Keep an eye on them and keep it progressing slowly. Good luck!

What is your neutral space? I like to use the bathroom where the floor is different, the space is small and I can control everything. I suggest changing space now that your male has associated where you've been trying to bond with a bad experience or at least wash it and move things around. Maybe wait a few days to try again. If you're only giving hay, I would also suggest using better food as a 'peace offering'. Hay isn't great enough, it won't catch their attention. When I bond, I go carrot and parsnip cut in small pieces and pellets and give a big pile of different greens so the rabbits are too busy making sure to be the first one to catch the best piece of vegetable to chase each other. And you know... people and animals alike are always friendlier with their belly full ^^ You can put a small drop of (not too strong) perfume on their nose to neutralize the smell. I don't endorse the 'stress' approach of bonding and I always try to turn the meeting process into some kind of great 'all you can eat' party so there is a positive association in their mind like 'isn't it great Thumper is there? LOOK what he brought with him!' The fact that the female started mean and dominates the process is normal, though. Once she is convinced the male won't try to contest her authority she will let up.

This is great advice, thank you! I have changed the neutral space ( was originally the bathroom, and is now the kitchen of our caravan , small and very different) and things seem to be a lot better. She is now grooming him, and they both seem very settled and are washing themselves and eating in front of each other. I did some carrots and cabbage scattered around and it seems like she has stopped being so nasty to him. There is is no mounting though, and she does have a good nip at him occasionally, and he scrabbles off, certified, but he is the one asking for grooming and she seems to be responding to him, so fingers crossed. Thank you again. It is always so reassuring to have such confident knowledge to turn to.

Occasional nipping is normal as long is it isnt to aggressive