Reverse thrust question

[vw_nutter]

Hi

Just going through ATPL exam revision for Powerplant using latest cae oxford books. One of the answers doesn't seem right for reverse thrust (blocker doors).

Question: Once the blocker doors are fully deployed, with an increase in rpm, which of the following statements would be incorrect?

a. Forward thrust from the hot gases would increase.
b. Forward thrust from the hot gases would decrease.
c. Reverse thrust from the blocked air would increase.
d. TGT will increase.

I thought a. would be correct, as with blocker doors, the cold airstream only is reversed and not the hot air. So if you increase the RPM, then surely the forward thrust from the hot gases would increase in-line with an increase in turbine speed, although the overall net thrust would be in reverse due to the larger amount of cold air thrust from the fan? Or am I reading this incorrectly? The suggested correct answer is b.

Thanks