That is expected based on the logic. It takes into account what the bot rolls and provides a different amount. This is not just a static win value.
range = $.randRange(1, 100);
winRange = $.getIniDbNumber('gambling', 'winRange'); // !gamblesetwinningrange
winSpot = (range - winRange + 1);
winnings = Math.floor(amount + ((amount + winSpot) * gain));
This way, depending upon the luck of the user, if the random number is higher, they will have more winnings.
When this was originally designed, we were asked to not provide yet another static win module but rather something a little bit more dynamic.