Mafia stands for Majors First Always. Not so common these days. Old Acol used to open 1H with a 2-4-4-3 16 count but many would open 1D these days.
In responding to a natural 1C, “Walsh style” advocates bidding the major before diamonds, even maybe with 4-6.
Canape opening systems would open 1H with 4-5 reds but not that they might open 1D with with 5-4 reds and extras, planning to canape into 2H next time.
Scamp is not a canape system, it’s a Mafia system. That affects responses and rebids.
Say you play Relay Precision with 2-over-1 non-forcing. (So 1NT is the relay) You open 1H with 3-5-4-1. Partner responds 2C non-forcing. This is an easy 2D rebid.
Compare the same auction in Scamp. Opener feels like rebidding 2D but that is unwise. This sequence needs to be reserved for 4-5 (or 4-6) in the reds. You can’t have it both ways. Responder needs to know what to do with 2-2 reds.
So opener passes 2C with 3-5-4-1. This in turn affects the responding style. If opener will often pass with a singleton, responder’s suit needs to be up to scratch, so a 6-carder or very chunky five.
1D – 2H is clearer. Opener can bid 2S/3C/3D with six but will pass on other hands with a stiff heart: 4-1-5+3, 5-1-4+3. That’s four hand shapes that will pass. So 2H is always six. This might help opener raise/
