Tahm don't use your shield so often !

Tahm kench's grey health regenerate back from 20% to 44% of it. Up to 55% with the strongly recommended .

When shielded, you don't only give up that regenation, but also the grey health you would have generated during that time frame. Unless it's a life or death situation or you manage to tank 100% of the shield (but it' s unlikely since it decay quite fast) It's often better to just tank everything and let the grey health regenerate.

Also the health regenerated can once again produce grey health while the shield is lost forever. Assuming you can reuse your grey health 3 time your new regen is 24/34/45/57/71 and up to 101% with spirit visage. Tanking reliably the same grey bar 3 time might be a bit tricky, but that's what a good tahm player should aim for.

Tier \ Shield usage 0.00% 50.00% 100.00% Thick Skin Tier 1 24.800 -12.800 -50.400 Thick Skin Tier 2 34.518 1.776 -30.965 Thick Skin Tier 3 45.517 18.275 -8.966 Thick Skin Tier 4 57.927 36.891 15.854 Thick Skin Tier 5 71.878 57.818 43.757 With Spirit visage 101.888 102.831 103.775

As you can see, When you use your shield you give up the capacity to produce more grey hp with that grey hp you spent. The only reason you'd use the shield is if you are about to die if you don't. Otherwise you will prefer to keep that grey health take it easy for a few seconds and come back to the fight as if no damage was dealt to you at all.

Doesn't count it was just the grey hp...