Follower sizing: multiplier or exact quantity
Every follower row on Copy Rules has a Sizing choice and an Amount field. Two modes exist for new rows: Multiplier and Exact quantity. Here is exactly what each one computes.
The multiplier formula, in plain words
The follower's target position is:
- Leader net × multiplier. The leader is net long 3, the multiplier is 0.5, so the raw target is 1.5.
- Rounded half away from zero. 1.5 rounds to 2. 0.5 rounds to 1, and -0.5 rounds to -1. Never banker's rounding — sizing stays predictable.
- Reversed, if the Rev tick is on.
- Clamped to ±Max — the follower never holds more than the Max value, long or short.
MirrorFill then orders only the difference between what the follower holds and that target. That is what delta-exact means: partial fills, scale-ins, and reversals stay correct by construction.
The multiplier field accepts a minimum of 0.1, in steps of 0.1. A zero or negative value is refused at Save: "the multiplier must be above zero."
Note the rounding floor: at 0.5×, a 1-lot leader trade still puts 1 contract on the follower, because 0.5 rounds up to 1. A follower cannot trade fractions of a contract.
Exact quantity
Exact quantity ignores the leader's size and copies only its direction. Set it to 2 and the follower holds exactly 2 contracts long whenever the leader is long, exactly 2 short whenever the leader is short, and flat when the leader is flat.
Two consequences worth knowing:
- Partial scale-downs don't touch the follower. If the leader trims 3 lots to 1, the follower stays at its 2 — the direction never changed.
- Flat stays flat. The follower only ever exits when the leader's net crosses or reaches zero.
The field must be a whole number, 1 or more. Anything else is refused at Save: "the exact quantity must be a whole number of contracts, 1 or more."
Balance-ratio sizing is legacy
Older followers may show a third option, Balance (legacy) — sizing by the follower/leader balance ratio. It appears only on rows that already have it stored. New rows choose Multiplier or Exact quantity. If you switch a legacy row off balance sizing, the option stays available on that row until you save it in another mode.
Quick answers
What does 0.5 round to?
- Rounding is half away from zero, so 0.5 becomes 1 and -0.5 becomes -1. A 0.5× follower still trades 1 lot against a 1-lot leader.
Which mode should a small account use?
Exact quantity is the simplest guardrail: the follower trades a fixed size no matter how large the leader goes. A multiplier below 1× scales instead, but remember the rounding floor. Either way, set Max as a backstop.
Where did balance-ratio sizing go?
It is legacy. Rows that stored it keep a "Balance (legacy)" option; new rows offer Multiplier and Exact quantity only.