I think you have two problems here. One you're using an 'ink' and i find for the FFG effect simple acrylic paint mixed with water to the consitency of semi skimmed or skimmed milk is perfect.

Its just far less harsh.

Then dont put in on and leave it to dry, it WILL puddle and clump

Swab it on the model them IMMEDIATELY drag it off gently with tissue or kitchen towl and it will draw off the excess and only leave it in the recesses with the odd grimy smear on the top surface.

My scyks as an example and it usually comes out better than this, i did these in a real hurry.

Straight nuln oil on white is way too harsh of a wash for me. You're going to get very blotchy results since every pool of black will show up.

Use Agrax Earthshade or even multiple washes of the Gryphonne Sepia equivalent.

Those scyks have gryphonne sepia watered down on the orange parts to give them a bit more depth, great wash

I've never tried it myself, but I've seen people swear by giving the mini a gloss coat before using a wash. Supposedly washes just slide right into the cracks and panel lines because there's nothing for it can hold on to on the flat surfaces. A matte coat afterwards will undo the shinyness of the gloss.

I also forgot to mention a really nice tip I picked up for shading x-wing models. The edging on that K's wingplates is, like loads of other models, really nice and important for suggesting the size of the ship. I use a graphics fine tip pen to draw in neat shadows along the edge. It looks really sharp, especially on the starviper, firespray, etc. I use a realllly thin nib, 0.03mm I believe. Not so good for detailed areas like engines, but if you're looking for some easy 'pop', a pen is a useful and cheap addition...

I've never tried it myself, but I've seen people swear by giving the mini a gloss coat before using a wash. Supposedly washes just slide right into the cracks and panel lines because there's nothing for it can hold on to on the flat surfaces. A matte coat afterwards will undo the shinyness of the gloss.

It's not so much "sliding into the cracks" but the gloss seals the roughness of the flat paint. An example would be dropping water onto a sheet of paper. The water soaks in, giving very little time to move it around. Swap out the paper for waxed paper and you have an idea what the gloss does for the wash. You also get why soap or alcohol is needed to break the surface tension. If you add some satin or gloss varnish to your paint you'll be able to skip the clear coat but your extending the drying time of your base coat.

With the gloss coat applied you can flood the wash over the model and remove it from where you don't want it ie. Raised areas vs recessess. A little retarder will extend the working time so you don't have to rush.

I use undiluted Vallejo Black Shade Wash. I cover the entire model and then use a cotton swab to soak up the excess from the raised areas. I've been happier with the results I'm getting when compared to Nuln Oil.

One crude trick for edging is just to use the long edge of an X-Acto blade to scratch off the paint so the plastic shows through. Works well on the noses of X-Wings and Headhunters, and anything else with sharp edges. If I'm careful I can also pick out the edges of certain small panels the same way.