My team is also in D.IV and i have the best defense in my league so i believe if you took my advice you would see some great results. First off i would simply try to find 2 SF's that can defend inside and Out. for instance on my team I have two SF's that look like this:
5k SF:
Inside D- Prominent
Outside D- Tremendous
6k SF:
Inside D- Prominent
Outside D- Strong
These are there full skills if you want to try to find a few players like them: They help soooooo much because it gives you options to set them as backups in 2-3 different positions because the first one can guard PG, SG, SF, PF and the second one can guard SF, PF and guards if your playing a bad team.
Weekly salary: $ 5 342
Role: draws a paycheck
(BuzzerBeta)
DMI: 19100
Age: 26
Height: 6'0" / 183 cm
Potential: superstar
Game Shape: respectable
Jump Shot: mediocre Jump Range: inept
Outside Def.: tremendous Handling: respectable
Driving: respectable Passing: average
Inside Shot: respectable Inside Def.: prominent
Rebounding: respectable Shot Blocking: inept
Stamina: pitiful Free Throw: strong
Experience: inept
Weekly salary: $ 6 397
Role: draws a paycheck
(BuzzerBeta)
DMI: 34400
Age: 31
Height: 6'7" / 201 cm
Potential: star
Game Shape: respectable
Jump Shot: mediocre Jump Range: average
Outside Def.: strong Handling: mediocre
Driving: average Passing: average
Inside Shot: respectable Inside Def.: prominent
Rebounding: strong Shot Blocking: respectable
Stamina: average Free Throw: mediocre
Experience: respectable
The last thing i suggest is to have one Defending big man and one scoring big man and then one defending guard and one scoring guard. this way you have balance.
Murray/Harris/MPJ/Grant/Jokic - 2020 NBA Champs