Lem's 101 says 1 to 2% bankroll plays are the maximum.
And though I tend to bet a play range that is a bit based on the old Machine/Computer's ranking scale(Small, Regular, Medium, Large, X-L),
most here will probably agree that flat-betting is best for most bettors.
Also depending on the player or group, size of play can be differing due to amount allowed to fill-up for at said number, also some play differing amounts on sports of their expertise(regardless of their bankroll's size, ability to rank-and-file better plays, or betting limits allowed)..plenty of variables.
Developing an eye for queer lines, and setting one's focus on finding "live dogs" as 60 to 75% of one's plays is my own personal opinion, developing the discipline to pass action is an absolute must, and developing a feel for knowing when to get in(volved), and when to get out is paramount..as every year has stretches where players get hurt(even wiseguys)..like after the MLB All-Star Break before the playoffs, when many pull up to recharge for the fall, it has busted and hurt many over the ages,etc..