Depends why you deload. Is it nutrition? sleep? form?
With linear programs especially when you're a novice- deloads are useful.. particularly when you need to correct your form... If it's your form you should always deload using submaximal loads (60-70% of your training max). So if I were squatting with a working set of 250 the week before. My deload week would consist of doing 165-175 at maybe 10 sets of 3-5reps. The high volume reinforces the squat groove and allows you to focus on where you are more explosive out of the hole without frying CNS (always record a side angle of all your lifts).
My squats are in the high 300's now at 170lb body weight. But when I was doing a SS/SL type of program in the beginning, I probably deloaded a good 5 times during the first 4months squatting low-mid 200's. You're going to feel down like a failure when you stall.. especially if you stall so early. You're going to want to give up on the program and be unmotivated to lift.. But you gotta be in this for the long haul.. it's not a sprint its a marathon..
I deloaded when I either stalled, had incredibly sore legs/hip flexors, or calves were locking up out of the hole. People say you should take at least 6 months perfecting your squat. I agree 100% especially if you're a novice. I know people that have been squatting for over 7 years and they are still honing their low-bar technique.
For the longest time on squats- the "cue" of pushing with your heel was a bad cue for me.... I don't know why but when I descended on the squat none of my weight distribution was on the balls of my feet thus I couldn't push with my mid foot. I was always told ''heels, heels, heels.. HIPS BACK''.. thus always drove down/pushed with my heels and outer portion of my feet. This one simple cue created a chain reaction of really bad habits that were hard to get out of. It created a very exaggerated vertical shin angle and caused me to sit back A LOT.. thus causing all sorts of hip flexor pain.. inconsistency in hitting depth...hyper extending at the lower back..etc..
However, I'll never forget my 5th and final deload as a novice on this program.... it just kind of "clicked". I stalled at 240 the week before. I was doing my original deload work at 10sets of 3. I was like WTF? I was smoking every rep till my 10th set. Feeling motivated I threw 240 on there beltless. Smoked it for a set of 5. Threw 250 smoked it for a set of 5. I was amazed. I started up the program again the following week at 250 rather than 240. I ran this program for good month and a half and stalled at 345lbs while maintaining 170lb body weight.
So to answer your question deloading 30% is unnecessary especially if you're squatting less than 2 plates. It's most likely a form issue. Sorry for the long response ha