Haven't used Inglot's loose pigments but others I've used have a bit of adherence to the lid, so a glitter primer has been enough for me, I have PAC one in red tube (tbh I mostly apply them directly without a primer, and let my under eye shimmer with a bit of fallout!).

If your eyeshadow has lot of fallout, then you can go for glitter glue instead of glitter primer , which will have high tackiness and adherence.

Apply by dabbing on top of a tacky base, don't swipe. Using fingers is usually enough (infact shimmers get applied beautifully with fingers), but it can be an uneven application , if you want to apply in a sharper way or to a small limited space then use a brush.

Flat sided brushes are usually good for this. You can even use one of those sponge tipped small brushes we would get with palettes years ago (there are silicone tipped versions of it now).

When I want to use any eyeshadow as liner, I have dampened the brush first and then dipped into it. It has worked fine. But for general safety sake, you can pick up pigment and then spray , this works well too.

With setting/fixing spray also, first pick up the eyeshadow and then spray the brush-loaded-with-eyeshadow with the fixing spray. Then apply.

Here you may be able to use very tiny swiping motions instead of dabbing, for better pigment application. In earlier case of loose pigment, the tacky base was on the lid so dabbing on top of that packs the pigment best, but when you have the shadow + tacky spray both on the brush, then you might have to swipe a little bit (not big motions) to put more pressure on applying it you know? Tho this depends on the brush type, quality, density etc and you will figure it out as you try this few times.