>>531002043
I guess your main problem is your insistence on combining the description of materials and the summon procedure.
To which I just need to show you Super Polymerization.
All fusions are inherently capable of using monsters from either field as materials if you use the right summon procedure, and unless explicitly mentioned otherwise.
In Super Poly case, the summon procedure said you can use monsters on either field, so you can use monsters on either field.
In Chimeratech Fortress case, you're using its own summon procedure that is listed on the second line of text saying you can use monsters on either field, so you can use monsters on either field.

They can of course specify it and said "monsters from either side of the field", because you can only summon Chimeratech using its own summon procedure unlike Alba-Lenatus, but I imagine they want to keep it open enough so future cards that interact directly with the materials listed on fusion monster like Over Future Fusion still works.
Because monster in your deck is not monster on either side of the field after all.