A follow-up question re: the 40% threshold.
Is the 40% threshold applied to the total number of hours you are working for your client(s)?
An example, I have 1 main client, for whom I do with 3 days onsite & 2 days from home office + 2 another clients which between them generate me the equivalent of 3 days work a week (weekends + evenings + 'holidays') on average. Work for these clients is all from home office.
Therefore, I am billing for 8 days a week on average and only on clients' sites for 3.
If the equation is % of time per client, then I am above it i.e. 3/5 days for main client but if it's % of total working time it's 3/8 which is below it.