ORIGINAL: Alvaro Sousa
I could do something like 2x the terrain cost landing. Let me think about it. For infantry it works fine. But at the same time he didn't garrison the entire coast.
Alvaro, I am not so sure that Sveint didn't garrison the entire coast. At a minimum I believe he garrisoned all of the ports. But even if Sveint didn't garrison the entire coast, the only consequences he should be made to suffer for his foolishness are those that are historically realistic/possible.
As a stupid example, lets assume that there were no limits on how far airborne units could be paradropped. After the US is in the war it transports most or all of it forces to Europe. The Axis player takes advantage of this by dropping 6 paratrooper corps stationed in various locations around Europe into New York, Washington, Philadelphia, Boston, etc. (sort of a Nazi Dawn). The Allied Player complains about this and everyone says "What are you whining about, you could have easily countered this by garrisoning all of your US Cities with a division each." On the one hand they would be right, the Allied Player knew the Rules and was stupid to leave the US devoid of any units. But at the same time, allowing paratroopers unlimited range would not have been historically accurate. I assume it is because you want the game to be historically accurate that you did give paratroopers a set drop range. This is why I hate it whenever something historically impossible happens in the game and people respond by saying there is a counter to it. For me it is irrelevant if there was a counter or not, impossible things should just not be allowed.
But enough of my rant. I like your idea of making units pay 2X the terrain cost. But actually I don't even think this is necessary. All that is required is that a unit pay 1X the terrain cost for the invasion hex/beach. As you can see from the screenshot above the armour was able to invade the mountain hex and still have its 1/2 OPs remaining. In other words, with the current system a unit pays no OPs for the invasion hes itself. But if you did this then I think you would need to round up the OPs a unit gets rather than rounding down. Otherwise and invading infantry corps with only 2 OPs would use 1 OP for the invasion hex/beach and 1 OP to attack, so it wouldn't have any OPs left to advance into the vacated hex if it's attack retreats the enemy unit.