They have other sensory organs on their heads.
Mine can't be the only ones that do a fair bit of tongue flicking when periscoping can they?
And, to be honest I have absolutely no idea on how effective at a given range their heat pits are. Obviously, good enough to hunt with at close range with poor vision and poor light. But, I can't make an reasonable guess on if they may or may not work over distances that benefit from that behaviour.