Canyon Stitched Jump bike headset bearings too tight to refit

Canyon Stitched Jump bike headset bearings : incredibly tight

I'd appreciate any advice on how to persuade new headset sealed bearings to go into my son's 2019 Canyon Stitched 360 jump bike as they (and the old ones) seem impossibly tight to get in

We had a lot of problems getting the old ones out as they were incredibly tight in the frame (more detail on this later) and although the new bearings are identical in size to the old ones they are proving impossible to get in even when using a very thin layer of grease to lube them with.

I've double checked the dimensions of the old and new bearings with vernier calipers and they are the same to within 0.01mm, and in any case we cant get the old bearing shells back in the bike either so I don't think the new bearings are at fault. (if its any help, these are the new ones we bought - https://www.airevelobearings.com/product/canyon-exceed-headset-bearings/)

The headset is a zero stack one with a pressed-in cup at the top and the bearing pressed directly into the frame at the bottom, it's very similar to the headset on his mountain bike however on the MTB the bearings were 'finger tight' - i.e snug but moveable and were straightforward to remove and replace.

We had huge problems getting the old ones out of the Stitched because they were incredibly tight in the frame. The bottom one eventually came out after carefully tapping all round with a drift but to get the top one out we had to take the bike to a local shop who drifted out the pressed in cup. Once we got that home we used heat to expand the cup and the remains of the bearing came loose.

The local shop said they think the new bearings should just slip in and don't want to attempt to press them into the cup and frame as they don't think this is how they are supposed to be fitted.

So... does anyone have experience of replacing these bearings on a Stitched, and/or any suggestions as to how we could persuade ours to fit, and/or any opinions about whether they should really be this tight ?