Hmmm....sounds like it could be something like tight packing/folding which can squish force some bleach up & out of foil placement resulting in a no heat weaker outcome where processing power is way weaker only lifting to a lv.6-7 raw in a band....too much bleach in foil maybe!?.....thicker bleach maybe!?..... I will outline what I do next to see if any technique may help you...
After weaving hair to be in foil, pull hair upwards/place pintail comb with foil (fine grade foil is easier to manipulate) lined up directly under pulled up hair to be bleached/ bring hair down over pintail with foil & give the comb a slight jiggle upward as you bring hair downward. This gets right to scalp by using the sectioned hair to fold the foil over the pintail for precise placement.
I use a color brush that has shorter bristles than average by 1/2 the regular length(you can cut a standard brush in half the length) especially on finer hair types. Don't load too much bleach on brush/ first apply bleach 1/2"-1" from scalp to remove bulk of the bleach/using corner of the brush vertically, lightly touch root @ scalp & sweep downwards twisting brush horizontally to standard position going downward right through first touch of bleach applied & beyond. Apply more if needed through rest of length starting in the sweep downward./ fold foil in half once/ run comb lightly across folded foil/ use comb tines to dent 1 end vertically of foil/ tap 2× the dent folding it over to close the side. Can repeat on other side of foil if needed or skip other side if not needed(easier removal 1 side closed only) I always leave a veil or thicker section between foils unless special case like corrective coloring or full color panel sectioned coloring+few foils.... Hope this works for you!