[shevek]

How would you play

1♥ - 1♠
2♣ - 3♥ ?

where 1♥ = 4+♥, not 4♠s, 11-15
1♠ = 11+ relay
2♣ = balanced

Responder can bid 2♥ to invite; or continue relay with a good heart hand; or have bid 2NT as a raise first time.
So 3♥ is not needed. We play it as shortage.

Being forced to open a major with four small can give responder doubts about 3NT.
"Is my singleton facing KQTx or xxxx?"
We have found that hands with a singleton do better to show than ask. Let partner decide.

Here's a (slightly doctored) one we had recently

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Overdoing it, maybe. Would be happy to reach 5♦ and find North with ♥AQTxx.

We have extended this.
In relay auctions, ALL 3-level breaks (opposite a bid that shows balanced) show shortage.

1♥ - 1♠
2♣ - 3♣/♦/♥/♠ show shortage.

Invitational hands with a long minor would have responded 3♣/♦ initially. (Or bid 2NT/3NT/relay now)

We do the same in strong club auctions:

1♣ - 2♣ = 8+ balanced with a major
3 any is a splinter

David Morgan points out that these should really be transfer splinters to give extra options to both.
You might even bid this way with a 6-card major

♠AKxxxx ♥x ♦KQx ♣Axx

When partner shows 8+ bal, this hand would like to show a mild slam try with six spades and a stiff heart.

[nullve]

 shevek, on 2021-January-25, 21:19, said:

2♣ = balanced

And still 11-15?

If so, how would you bid with. say,

a) 11 hcp and 3424 opposite 11 hcp and 4243
b) 15 hcp and 3424 opposite 7 hcp and 4243

?

Maybe

a) 1♥-1♠; 2♣-2N; P
b) 1♥-1N; P

?

[shevek]

 nullve, on 2021-January-26, 02:12, said:

And still 11-15?

If so, how would you bid with. say,

a) 11 hcp and 3424 opposite 11 hcp and 4243
b) 15 hcp and 3424 opposite 7 hcp and 4243

?

Maybe

a) 1♥-1♠; 2♣-2N; P
b) 1♥-1N; P

?

Yes. We pass some balanced 11-counts. Not a good look to play 2NT with 11+11.
When you focus so much on shape, there is a cost.