1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

for _ in range(int(input())):
    n=int(input())
    a=list(map(int,input().split()))
    s=set(a)
    if len(s)==1: print(-1); continue
    mx=max(a)
    if a[0]==mx and a[1]!=mx: print(1); continue
    if a[-1]==mx and a[-2]!=mx: print(n); continue
    for i in range(1,n-1):
        if a[i]==mx and (a[i-1]!=mx or a[i+1]!=mx): print(i+1); break