As the title of the question requests, are there any compact ways to say to reduce the model to less than 25% of its original size?
The original phrase looks weird.
Before providing actual phrases to directly answer you question, I would like to digress slightly, explaining why the phrase you chose looks weird to you.
Specifying the destination percentage of (less than) 25% generally requires a mental calculation to derive the delta, or difference, in size from the original. It's generally easier for people to comprehend percentages as deltas. Whether this is human nature or simply the result of convention, or both, I really can't say.
This can be clearly seen in the choice of preposition: 'to' versus 'by'.
Consider the following example:
I reduced my weight to 80% of my original weight.
Tautological, and more focused on the original weight, instead of how much you lost.
I reduced my weight by 20%.
Succinct, intuitive, and focused on the loss.
That said, to reduce the size (pun intended) of your original phrase, we can apply several strategies. Let's start with re-stating it before whittling:
reduce the model to less than 25% of its original size
The most obvious, as already discussed, is to explain the percentage in terms of a relative difference, or delta. Which leaves us with:
reduce the model's size by more than 75%
Next, we need to decide if any combination of these words can be expressed as a single word, and also distinguish between critical and optional words.
(At this point, the possibilities are bounded by the level of formality required. Unfortunately, I don't know if this is a dissertation, text message, or somewhere in between, so I'll provide you with some choices in the hope that at least one will be formal enough for your purposes.)
Let's assume that optional words are those that are required for grammatical correctness, but without which, the exact intention is not marred in any way.
'the' is really the only optional word, unless, in the surrounding context, you can refer to 'the model' as 'it', but I won't make that assumption yet. We can remove the 's on model, further compromising the grammar. So, now we have:
reduce model size by more than 75%
Looking for combinations of words here that can be expressed more succinctly, I immediately see 'more than' can be expressed as a symbol, '>' (this would not work in spoken language, however.):
reduce model size by > 75%
Another combination of words that reduces nicely (more pun fun), but is not immediately obvious, is 'reduce' & 'size'. The idea of reducing size cannot really be expressed more obviously and efficiently than 'shrink' (kudos to @TRomano for this one):
shrink model by > 75%
Now, interestingly, 'by' becomes optional (arguably) because of the expressive power of the word 'shrink':
shrink model > 75%
Going to the extreme, if you can be certain that the reader (we've assumed text at this point) can deduce from the context that you are referring to 'the model', then you can do:
shrink it > 75%
Depending on how clear the context is, you could even remove the direct object, 'it' (we're really pushing it now):
shrink > 75%
Pursuing this further is probably pointless, but just for fun:
shrink > ¾
Removing the spaces (still readable in my opinion):
I just reduced the size of your original phrase by more than 85%. Or to less than 15% of its original size, depending on how you want to look at it... ;-)
A ¼-scale model is succinct. Or as John Lawler has pointed out, a quarter-scale model.
- Reduce model size by at least 75%.
Compact and colloquial: shrink the model at least 75%
Reduce the model (size) by at least 75%