I agree you should think of yourself as a 4:30 miler for now. You ran 4:40 a year ago as a soph, so just normal maturity plus your decent training should have you 4:30 this year. Until you break 4:30, train as a 4:30 guy. Plugging 4:30 mile into Tinman calculator gives you the following training paces:
Tempo: 5:35
Threshold: 5:20
CV: 5:05
I will now design your workouts for free:
TEMPO:
So we see you are basically spot on with your tempo paces, not too slow like the one poster said. I agree with the other poster you should do tempo runs as continuous runs, not reps. Or 2 blocks of 15 minutes each with 5 min jog between. So either:
1. Warmup + 5 miles straight @5:35 pace + cooldown.
Or
2. Warmup + 15 mins @5:35 pace +5min easy+ 15 mins @5:35 pace.
THRESHOLD:
5:20 pace for you. I advise doing repeat miles with short rests , or 2x 10 minute blocks. So either:
1. Warmup + 4x 1mile@5:20 pace with 1 min rest + cool down
Or
2. Warmup + 2x 10 minutes @ 5:20 pace with a 3min easy jog between + cool down.
CV:
The pace made famous by Tinman. 5:05 for you. Just copy his 4x 1k @5:05 pace with 1 min rest.
I advise you follow each of your workouts (before cooldown) with 2 400s and 2 200s at 4:30 to 4:20 mile pace (so 68 to 65 for the 400s and 34 to 32 for the 200s).
Let's plan you a week:
Keep your same Tuesday, Thursday, Saturday workouts, but turn them into one tempo, one threshold, and one CV plus the 400s and 200s). Alternate the tempo and threshold options each week. Mon wed and Friday run easy (do not exceed 7:00 per mile, followed by 8x 100m strides). Sunday run 12 miles easy, with the last 3 miles hard only if feeling great.
So example:
M: easy + strides
T: tempo
W: easy + strides
Th: threshold
F: easy + strides
S: CV
Su: long
Do this week in and week out, and you will be an aerobic beast who has ALSO done tons of mile pace reps, and you will kick as$.
Now go make me proud.