I don’t know who told you about HIGH[0] or where you read it, but it’s wrong whatever!
[0] or NOTHING means the current bar (the one just closed, before the new one opens), so the bar before the current one is identified by [1].
If you are using daily bars, at the end of today’s bar you strategy is executed, just before the new bar opens, so the bar tagged July 4th is the CURRENT bar identified by [0].
I never dealt with pyramids, I know you can find several pieces of code about it searching this forum.
In any case if you tell me what you want to do I’ll try to help.