I have great respect for
@GC-Raptor 's experience, but will differ on this issue. You will find me in the camp of
@JacinLarkwell and
@Folly's place on this subject. Particularly as you are choosing a low protein layer feed as their complete feed.
Some "thumb rules" and quick approximations since I don't know what scratch brand you are using. Together with some broad averages, for purpose of illustration.
An average hen, under average conditions, is estimated to eat an average of 1/4# of feed daily. You have four birds, so that's 1#, or 16 oz total, each day. The "thumb rule" for treats is not to exceed 10% of diet, by weight, daily. It exists not because its correct for every circumstance, but because its conservative enough to prevent the majority of harms, in the majority of circumstances - that is, its "good enough".
Layena Crumbles (Pellets are substantially identical) have a nutrition profile of 16% Protein, 6.5% Fiber, 2.5% fat, 4% +/- Calcium, .7% Lysine, .3% Methionine.
For reference,
UGA suggests target figures of 16-18%, 3-4%, 4%, .8%, .4%. You can find similar figures from
NRCS/USDA and
others. Layena begins as a borderline feed (that's *normal* for layer rations, cost is a big component of layer feed design).
Purina's
"Scratch Mix" offers a nutrition guarantee of 8% protein, 4.5% fiber, 1.5% fat, .1% calcium and says nothing about amino acids (nor could they, as the ingredients vary - "Freshly-ground North American grains")
You are offering 4-5 oz of scratch daily, plus some negligible and nutritionally uncertain (and seasonal) free range time. That's a great unknowable I'll disregard.
If the chickens substitute scratch for complete feed (sticking with the 1/4# total per day), 25% of their daily ration is Scratch! ENd result? 14% Protein (too low), 4.5% fiber (tolerable), 2.25% fat (too low). Calcium is tolerable. We can guess at the aminos if we have to, based on the likely grains included (cracked corn, milo, red millet, sunflower seeds) in the scratch - could be worse, not exceptional. If chickens, in accordance with pecking order, only pick favorites out of the scratch, the likelihood of nutritional problems grows accordingly.
If the birds add the scratch to a normal ration, their caloric intake goes up (and your total feed costs with it), but no benefit (beyond their entertainment, and your ability to encourage them to dig different areas of the yard) comes of it. The scratch isn't improving anything - and (fingers crossed) their brief free range time is compensating.
I prefer a little more certainty, and I say that as one who free ranges my entire flock daily, dusk to dawn.