question about small vocal booth

[grignacarbo]

hi everyone, I created a vocal booth based on the bold parameters. The vocal booth is 130cm wide, 200cm long and 290cm high.
For the acoustic treatment, I filled all the walls with 15 cm of 50 kg density rock wool, over the rock wool I put a thin plastic and finally the camira cara fabric. In one of the walls (the 130 cm one) I created a slat wall in order to absorb mainly the frequencies from 150 to 300 hz.

Question number 1: I took a cue from john sayers' vocal booth for acoustic treatment, but I noticed that following that type of project the decay time t30 is under 70 ms seconds, ebu tech recommends having a decay time greater than 120 ms, so does it matter to increase the decay time? it seems that john doesn't make almost everything absorbent in small rooms, although putting the plastic will increase the decay time only on the high frequencies.

Question number 2: Should the decay time t30 be flat? I was able to get a fairly flat response by removing the plastic but it sounded too boring, I like more to raise the treble above 6000 hz, also it seems that it sounds more pleasant by increasing the bass a bit, so I feel less effect annoying of the mids around 2000 hz

Many will say that a small vocal booth does not work, I have seen john's vocal booth sound very good, but I cannot get the same results, what is wrong with my vocal booth? I am attaching the graph