During the last hour I have performed the following tests using my veritas medium shoulder plane which has an adjustable mouth. Varitas suggest that it can be used for end grain or for long grain rebates, hence the adjustable mouth. ( lovely plane by the way)
I planed end grain on some greenheart, lemonwood, and pine with a tight mouth. There were no major problems however the greenheart shavings were not continuous but the planed surface was smooth. The shavings were 2 thou measured with a micrometer.
The mouth was opened up to 1.5mm (60thou) the lemonwood was easier to plane in terms of effort however the shavings and finish were the same. Both the greenheart and pine remained the same as with the tight mouth. There was certainly no tearout ( I cant see how you can have tearout as such in end grain like you do in long grain).
The blade was honed at 28 degrees, the bed angle is 15 degrees giving a effective cutting angle of 43 degrees. All I can learn from the above is with these 3 species of wood and with this plane , the mouth size makes no real difference.