Can someone explain the new hills please

[Mobhack]

As Don says - no changes whatsoever were made to the core sighting code. Only to the detail reported on the info line.

Have you considered that your opponent might have had a decent vision rating - since troops with vision gear can see a bit further into smoke and dust, foliage, buildings etc as well. Especially units with thermal sights. Therefore though you could not see him, he may well have had no problems seeing you.

Or, you checked visibility to the enemy unit in your turn when there was some micro-smoke there (only smoke of a certain value or higher shows as smoke animations - micro smoke does not, but it can affect visibility especially in edge conditions) - and that had then cleared in the end turn phase. Or there was a smoke animation - but you had smoke off, or were relying on it sticking about - smoke can dissipate or in some circumstances, spread (usually from fires and wrecks). There have been plenty of times on a battlefield where I had thought my Sherman safe where it was parked (checked vision) - but in the enemy turn, the tiger slotted it due to smoke reduction, with the surviving crew being well able to see it (assuming it remained in the same hex!)...