30% erection level might leave you with a baseball bat shaped penis. If you are cool with that …
Sometimes you can’t help gaining girth but avoiding full erection is important. We know that full erection jelqing leads to girth gains, probably because the inner and outer layers of fibres of the penis are at right angles during an erection (see Brillant TED talk for the savvy aorund 8 minutes in) producing the stiffness in the erection but less resistance to growth in any direction. This might also be why some people find erect stretching effective. When flaccid the fibres are aligned at more like 45°, allowing the penis to bend more easily. So as you get closer to full erection the fibrous skeleton gets closer to 90°.
The trouble is that the lower your erection when you jelq, the more likely that you are simply pushing blood up during the lower half of the stroke and then the pressure gets greater and greater as you get closer to the end, leading to a baseball bat effect in gains. The idea with jelqing is that the pressure should be relatively consistent throughout the stroke, so with a lower erection level you need a looser grip. At some point in time this becomes useless and I think 30% is way too low.
You may find that doing the Newbie Routine will bring you the gains your require but consider adding a stretch at the end of each stroke so that you are encouraging length rather than girth gains and maybe stretching more within the routine as you go on.