Short answer: yes, they stack beyond that limit. 
Long story ahead… 
I just checked another combination consisting of Kirill (+30%), Tarlak (+100%) and Ratatoskr (shields enhanced by 64%). See video:
Concentrate on the bottom green combination after reshuffling. The left shield has Ratatoskrs bonus active, the others don’t. The combination hits:
The left tile hits for 900, the right one for 693 damage (ignore the middle one as it hits the weak point).
- The right tile has an attack boost of 30%+100%=130% added to the normal 100%. Hence 693/230 equals about 310 base damage (aka 100%).
- The math for the left tile then: 900 damage divided by 310 (better 3.1 per 1%) base damage results in about 290% attack or a 190% attack boost.
Remembering that there is an attack boost of 30% (Kirill), 100% (Tarlak) and 64% (Ratatoskr) this sums up to 194% and pretty good matches the calculation performed for just one single tile. As the maximum boost as given from Tarlaks description is 160%, the enhanced shields do stack beyond that.
Enough evidence for me to not further investigate a couple of hundred tiles. 