Hi Peter,
With most partners, I use rule of 20 even WITHOUT the tricks I mentioned earlier (multi 2D and acol 2 bids and "strongish" 3 suiters rolled into 2C/2D ). It still works in the long run.
Here is another tool you can use, especially if you lower even more the opening requirement...
Keep 1NT forcing,
Make 1M-2M "competitive" raise with virtually any 3 card support (1M-3M competitive with four card support, 1M-4M with 5 card support).
1M-2NT not so much jacoby, but limit raise or better
1M-jumpshift = fit jump, with suit, support, less than GF
1M-double jumpshift = splinter
1M-2C... either a) Clubs true game force,

balanced Invite, c) balanced game force, d) 3 card support constructive or better, e) 3 card support game force.
The 2C bid and the jump shift (fit jump) take a lot of pressure off 1NT. For instance, 1M-1N-2x-2N is no longer balanced invite (go through 2C). This means after something like
1H-1N-2D, you can define an immediate 3C as "good" and a bid of 2NT as lebehnsol leading to a weak 3C or weak 3D raise. Combine with the free 2S on this auction, and you have lot of descriptive bids. This good/bad 2NT without competition by responder helps unravel some of the strain put on 1NT by light opening bids. If you play the 2C structure and role the acol and three suited bids in 2c and 2d like I do, you can lower from rule of 20 to rule of 19 (or I suspect even good rule of 18) and survive the light bids. A side help, 1M-1N-2x-2M is always disaster... since weak 3 card raise immediate, and constructive or better through 2C's.
(BTW,,, I follow ETM victory for 1M-2C auctions, with any opener response but 2D as full game force, but sometimes I temporize with 2D with strong game try waiting for partner to clarify his holding). But Light opening cleary should be in your arsenal.
BTW, the rule of 20 follows in a formalized way what Misho said... "
This mean you must have at least 1 good 5 card suit, good 4 cards is not enough!". Good follows the rule for adding points for good intermediate cards, and five card suit needed to add up to enough "points" for the rule.
Ben