One Step Classic and One-Step Rapid are available in: $5K, $10K, $25K, $50K, and $100K account sizes.
Frontline Instant is available in: $10K, $25K, $50K, and $100K account sizes.
Higher tiers come with more drawdown and the ability to gain profits faster with the leverage on the higher balance.
For example (BTC or ETH at 5:1 leverage — the only pairs eligible for 5:1 on Classic and Rapid; all other pairs are 2:1, and Frontline Instant is 2:1 across all pairs including BTC/ETH):
On a 10K account, a 1% move in BTC at 5:1 leverage = $500
On a 100K account, a 1% move in BTC at 5:1 leverage = $5,000
For an alt at 2:1 on a 10K account, a 1% move = $200. See What leverage is available? for full details.