if you're in full check with both gloves (NOT arms) taking the impact and you are not moved, how would the opponent score from it? i presume they wouldn't? like so:
it would at best be a C score if it hits your arms, otherwise it would be ineffective? additionally if checked and the attacker loses balance from it while you stand strong, then it is an automatic non-score for them as well?
reference:
http://www.mymuaythai.com/wp-content/uploads/2015/03/Screen-Shot-2015-03-12-at-20.51.59.png
If you HAD to check a high kick, the ideal would be this upper body position with both feet planted. The impact should be dispersed across both forearms and and your rear upper arm. If you synch down and have your feet planted you won't be off balanced as much, and have a more effective counter. But you have to be sure it's coming high....
I know some advice to use the forward glove to "catch" the kick, but it tends to be the upper and lower part of the rear arm. I tend to use both forearms and upper arm.
As far as scoring goes, it has to be taken in context. Muay Thai in Thailand and at higher levels tends to score the fight overall, where as at lower levers in most of the rest of the world it's a 10points must system.
In Thailand, it would be gauged on how effective the technique was. So if it was off balancing the oppo, it scores. If it caused damage to the arm, it scores. If it stopped forward momentum, it scores. If the oppo was blasting him, quick check, then straight back to blasting him, it doesn't really count. The judge can wait till later in the fight to see if the technique is accumulating damage, or if it's just a point scoring tap.
In the 10 point must system the judge can't wait to see if the damage from the kicks are going to accumulate, they have to decide there and then and put a number on the card. That means that although a checked kick obviously doesn't score as highly as a clean on, it still carries a little more weight.
Also remember that there's no points for defence, only offence. You can check and slip all you like, if your not throwing back, you lose.