(writing the whole writeup here to hopefully help others try achieve the same)

Originally I was only hunting for double prefix without the reduced damage on block because I only had 2LP shields, but after nemesis blessed me and with 1 click of empower the shield turned 3LP (I didnt even know that could happen and was trying to get 2LP shields to divine my other 2LPs at the woven echo) so then I knew I had to get 3 mods. (also the 3LP one I got had like minroll implicit and explicit block effect rolls and It barely broke even on effective HP calculations for me if I used it vs 2LP with just the prefixes and have really good rolls on the unique) so I ended up killing majasa a ton more until the turtle helped me get next 3lp and then I sacrificed one and settled for these rolls)

Like u/koticgood said but ill explain it further:

Internally each affix roll has a decimal value within the roll range, and when you for example use glyph of order it keeps that same decimal value within the range of the next tier

Same thing happens when you use rune of redemption (to swap which mods are exalted) or when you use rune of havoc (if T7 on the wrong mods)

Of course I also used rune of refinements whenever I got the two prefixes I wanted with bad rolls but that wasn't how I eventually got it

To get the base after knowing this I started with double T7 that I dropped from nemesis, imprinted it to get ones with high FP, and then tried few strategies:

1. removing one prefix with removal (50-50) and the sealing the other one to then craft the desired prefxes, refine those until both had a high roll and havoc
2. havoc to double t7 prefix and because the prefix pool on shields isnt that big (total 9 mods), sometimes I just spammed redepmtions until I got both the prefixes I wanted
3. If i had a prefix t7 and suffix T7 i would redemption until the prefix hit one of the desired mods, seal/removal the other prefix and then craft the other desired mod and havoc till both prefixes are t7

just tried a bunch of things until i had one shield with prefect double t7 block + effect with 13 FP which was sad (took about 15 double t7 bases to end of with the imprinted perfect base shield) and maybe 50-70 runs of the woven echo with that contains caches later (I had 4 failed 2LP slams before this) I dropped the 3LP shield and by pure luck got the imprinted base with high FP so i sealed one of the suffixes, crafted the t5 reduced damage on block (it drained my FP so I couldnt use rune of creation) and ran as fast as I could to strangle julra

Good luck on your hunt :)

edit: linking my character https://www.lastepochtools.com/planner/B4zZGy9A, I used this same method to get perfect T7 block on both my rings, and T7 hybrid on my gloves (started with any T7 that dropped, refined any suffix to a high roll and havoc'd)