single word requests - Is there a counterpart of "sufficient"/"enough" meaning "not more than the needed maximum"?

I understand the meaning of the word sufficient like defined in Merriam-Webster:

sufficient = enough to meet the needs of a situation or a proposed end

So mathematically said:

not less than the needed minimum

Is there an "upside-down counterpart"?

not more than the needed maximum

It should be of the same style as sufficient or enough, expressing the same concept (being within limits and not being under the maximum).

Let's have an example of a chemical reaction. In order the reaction can start, you need at least 5% concentration of a given substance. So if the concentration is 6%, we say that the concentration is sufficient. (Also suggesting that no more concentration increasing is needed.)

However, what if the requirement is that in order the reaction can start, the concentration of the given substance should be at most 95%. So if we have 94%, the concentration is ...? Sufficient here sounds funny...

Analogically, it should also bear the notion of no more concentration decreasing is needed.

I am searching for a single word in the same common style as enough of sufficient, not for a mathematical expression.

N.B.: I do not mean the same as in the related question Can "sufficient" be used in a negative sense?

Answer

I think “sufficient” covers the whole range between insufficiently low (too low) and insufficiently high (too high), but I do agree that “sufficient” (and especially “enough”) can imply that the lower end of that range has been (just barely?) reached.

Just as, imo, “sufficient” covers the whole acceptable/sufficient range (with a bias towards the low end), so does “tolerable” cover the whole acceptable/tolerable range, but perhaps with the bias towards the high end that you are seeking.

“Tolerable”: adjective/ bearable, endurable, supportable, acceptable. (Oxford Dictionnaires)

Step 1: Insufficiently low/intolerably low (too low) = insufficient/intolerable/unacceptable);

Step 2: Sufficiently high/tolerably low (high enough/not too low) = sufficient/tolerable/acceptable;

Step 3: Tolerably high/sufficiently low (not too high/low enough) = tolerable/sufficient/acceptable;

Step 4: Intolerably high/insufficiently high (too high) = intolerable/insufficient/unacceptable.

The above steps are trying to show that “insufficient, sufficient, tolerable, and intolerable” can be used at both ends of the range of acceptability, but please note that the bolded words in each step are, in my opinion, ‘best suited for’/most often associated with that step.

Both “insufficiently” and “intolerably” use “low” in Step 1 and “high” in Step 4 to convey the meaning of those two Steps, which could mean that the bias towards either the low end (sufficient) or the high end (tolerable) that I perceive in these two words disappears when discussing unacceptable levels below and above the acceptable range.

Within the range of acceptability, however, “high” and “low” must be flipped to make sense of “tolerable” and “sufficient” as they are used in Steps 2 and 3, which, imo, supports the bias that I perceive and perhaps supports “tolerable” as the best one-word answer to your question.