As Will T. indicated - Hi-Lite/ Hi-Lok are designed for "light interference".
On thick stackups - ensure that the hole diameter is on the "larger side".
Is access available on the "head' side - use a alum/brass punch to hammer the fastener in.
In some blind locations use a MS21042-X nut with washer stackup to draw the fastener in - then replace with the correct collar.
- if all fails - verify the fastener & material diameters. Are you using reamers?
many techs / MROs use "custom" reamers skewed to the higher end of the diameter.
- last thing you want is to have the pin "pinched" in a blind location with no access to punch it out.
- errata : when installing in Stainless sheets - Holes were always to be on the "higher" side of the diameter. Whereas Alum pins were installed on the "lower" side.
- What Fastener diameters are u dealing with? Typ -6, -8 or -12 & up. Large Diameters always require "looser" holes - especially in thick materials.
- on initial insert - are any threads showing?
I would not "force" a pin in beyond typical effort. Something is just wrong. This will just cause issue - either to the pin or the material.
Also consider the poor bloke who may have to remove the pin sometime later. It you installed via hydraulics .. what is he to do to remove?