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()))
    ans=-1
    ind=0
    for i in range(1,n):
        if a[i]!=a[i-1]:
            ans=0
            break
    if ans==-1:
        print(-1)
    else:
        m=max(a)
        ind=0
        for i in range(n):
            
            if a[i]==m:
                if i>0 and a[i-1]<a[i]:
                    ind=i+1
                    break
                if i+1<n and a[i+1]<a[i]:
                    ind=i+1
                    break
        print(ind)
                
        
